Let me orient you — Page 440, Lesson 407

I want to walk you through what this page is actually showing you, because at first glance it looks like a wall of numbers — and in a way, it is. But those numbers are the entire point of this part of your General Navigation syllabus. This is a sunset table — a pre-computed table of the times of sunset, and in some cases sunrise, for a specific latitude band, laid out so that a navigator can read off the time of sunset for any given date without doing any spherical trigonometry in the air. Let me orient you. The page is headed 17 01 — that's the date, the 17th of January. The table is arranged in columns, and each column is a latitude. The numbers running down the left-hand margin — 10, 18, 27, 62, and so on — those are the minutes past the hour for the first entry in each row. The big numbers like 46 15 49 15 54 15 59 16 04 16 10 are the actual sunset times, written as hours and minutes — so 46 means 16:46, 15 means 17:15, and so on. The pattern repeats across the row, each entry being the sunset time at a successive latitude. Now, the key thing to understand is what the table is for. In navigation, you often need to know the time of sunset — or sunrise — at a particular position, because it affects things like night flying rules, fuel planning, and the legality of continuing a flight into darkness. The table gives you the local mean time of sunset for the date at the top, for a range of latitudes. You find your latitude, you find the date, and you read off the time. Let me trace one row so you can see the logic. Look at the row that begins 16 45 16 48 16 51 16 54 16 58 17 02 17 06 17 10 17 15 17 19 17 24 17 28 17 33 17 38 17 43 17 48 17 53. That's a full row of sunset times. The first entry, 16:45, is the sunset time at the lowest latitude in that band — the one closest to the equator. As you move across the row to the right, the latitude increases, and you can see the times getting later — 16:48, 16:51, 16:54, and so on up to 17:53. That's the physical reality: in January, in the northern hemisphere, the higher your latitude, the later the sun sets. The table is just encoding that relationship numerically. Now look at the rows further down the page. You'll see times like 19 07 19 08 19 09 19 09 19 09 19 10 19 10 19 09 19 09 19 08 19 07 19 06 19 05 19 04 19 02 19 00 18 59. Notice something interesting — the times rise to a peak around 19:10 and then start falling again. That's because as you move to even higher latitudes, you're approaching the point where the sun barely sets at all in mid-winter — the times reach a maximum and then decrease. The table captures that curvature. And then look at the very bottom rows. You see entries like S60 23 04 22 58 22 51 22 43 22 34 22 25 22 16 22 06 21 57 21 47 21 38 21 28 21 18 21 08 20 58 20 49 20 39. The S60 is a label — it tells you this row is for latitude 60 degrees South. And the times are very late — 23:04, 22:58, 22:51 — because in the southern hemisphere in January it's mid-summer, so the sun sets very late indeed. The table covers both hemispheres, and the S prefix distinguishes southern latitudes from northern ones. So the practical skill you're building here is interpolation. The table gives you sunset times at discrete latitudes — say, every 2 or 4 degrees. If your actual position is between two of those latitudes, you estimate the sunset time by interpolating between the two adjacent entries. The same applies if you're between two dates — the table is for the 17th, but you might need the 18th, so you interpolate between the 17th and the next page's table. One more thing to notice: the times are local mean time, not UTC, and not zone time. That's a crucial distinction for your exam. Local mean time is based on the sun's position relative to your meridian — it's the time a sundial would read at your longitude. When you use this table operationally, you'll need to convert that local mean time to UTC by applying your longitude correction — 4 minutes per degree of longitude — and then to your local zone time. The table gives you the astronomical fact; the conversion is your job. Let me also point out the structure of the rows themselves. Each row is a latitude band, and within the row, the entries are ordered by increasing latitude. The left-hand margin numbers — 10, 18, 27, 62 — those are the minutes of the first entry in that row, so you can quickly scan down the margin to find the row you need without reading every entry. It's a navigator's tool: fast to read, fast to interpolate, and accurate enough for planning purposes. So, to summarise what this page is: it's a sunset table for 17 January, covering a range of latitudes in both hemispheres, giving local mean times of sunset in hours and minutes, with the S60 label marking the southern-hemisphere rows. You read it by finding your latitude, reading the time, and interpolating if needed. And you always remember the times are local mean time — the conversion to UTC and zone time is on you. That's the whole page, and it's a skill you'll use every time you plan a flight that might end after dark.